On Monday 2 July, the CryoSat-2 spacecraft was orbiting as usual, just over 700 kilometres above Earth’s surface. But that day, mission controllers at the European Space Agency (ESA) realized they had a problem: a piece of space debris was hurtling uncontrollably towards the €140-million (US$162-million) satellite, which monitors ice on the planet. As engineers tracked the paths of both objects, the chances of a collision slowly increased — forcing mission controllers to take action. On 9 July, ESA fired the thrusters on CryoSat-2 to boost it into a higher orbit. Just 50 minutes later, the debris rocketed past at 4.1 kilometres a second.